This was just me trying to get it working, yes there would jsut be one customer.
I tried the following, but it also was a failed attempt:
if Input.cart.customer.orders_count < 1 push "New Customer" end
My understanding is that it should be possible to find out if customer is logged in and/or has existing placed order. So far I am just testing a draft script, so not sure if customer values are faked for demo purposes or not, either way, I am not getting new customer triggering any way I try.